This invention relates to measuring impedance at an electrochemical interface.
Electrochemical corrosion is a costly problem for many metal structures. In electrochemical corrosion, a bulk metal reacts with an electrolyte, resulting in loss of metal from the bulk. Metal atoms are removed from the bulk metal by an oxidation reaction at the interface, resulting in a net current flowing into the electrolyte. A reduction reaction balances the charge transfer process, generating a current equal in magnitude to the oxidation current but of opposite polarity.
The rate of corrosion is known to be related to the charge transfer resistance at the interface of the oxidizing metal surface and electrolyte. The charge transfer resistance is a measure on the difficulty in moving charged species across the interface between the metal and the electrolyte. Since metal atoms are removed from the bulk as charged species, the charge transfer resistance indicates the ease with which corrosion can proceed. It can be determined by measuring the impedance at the metal-electrolyte interface. Typically, this is accomplished by applying an external voltage or current across an electrochemical cell having a pair of metal electrodes immersed in a liquid electrolyte and measuring the response of the cell, from which the interfacial impedance is calculated.